This application claims the priority of Japanese Patent Application No. 4-349465 filed Dec. 28, 1992, which is incorporate herein by reference.
1. Field of the Invention
The present invention relates to a device for washing the ink rollers of a printing machine. More particularly, the invention pertains to a device capable of automatically washing the ink rollers.
2. Description of the Related Art
In general, printed materials such as pamphlets, catalogs and the like, are normally printed by an offset printing machine. The offset printing machine enables multiple color printing, and is suitable for producing a large quantity of paintings. The printing machine is equipped with a plurality of ink rollers which convey ink from an ink tank to a plate cylinder. The ink rollers are disposed between the ink tank and the plate cylinder, for feeding the ink from the ink tank to the plate cylinder. The ink used for printing, forms layers on the outer surface of the ink rollers. The ink on the rollers needs to be washed away before using ink of another color or after the completion of the printing operation.
Usually, an operator puts washing fluid on the ink rollers, and washes them. A blade is pressed against the surface of a lower roller, adjacent to the plate cylinder, to scrape off the ink from the surface of that lower roller, as it rotates. However, this cleaning work is cumbersome.
Some attempts have been made to improve the washing operation. One such attempt is described in the Japanese Unexamined Patent Publication No. 62-50145, which describes an ink washing device which automatically sprays washing fluid from a nozzle, by operating a switch. The ink washing device includes a tank containing washing fluid, which is connected to a nozzle for spraying the washing fluid. By operating a switch, the washing fluid in the tank is sprayed on the ink rollers. Subsequently, a blade is pressed against the outer surface of the ink roller adjacent to the plate cylinder in order to remove the layer of ink that deposited thereon.
The completion of the washing operation in the above washing device is determined by calculating the number of times N the ink roller is sprayed, or the period of time for spraying. In the Japanese Unexamined Patent Publication No. 62-50145, the number of times N or the period time of washing fluid spraying is preset, depending upon the ink condition of the ink roller surface. However, the condition of the ink on the ink rollers might vary, and the washing efficiency might not be equally efficient for different types of ink or washing fluid.
As a result, the washing operation could end regardless of the condition of the rollers, since the washing period or the amount of washing fluid is predetermined. When the number N is below an adequate level, the amount of the washing fluid sprayed on the rollers is insufficient, and the rollers are not cleaned completely. If the printing is resumed after such incomplete washing, the printing quality could become inadequate.
To avoid this problem, the amount of post-washing residual ink on the ink rollers must be checked by the operator. When the washing period is not long enough to clean the rollers, the ink rollers must be washed again. However, this operation is cumbersome, since the washing device needs to reset the washing period several times until the roller is properly washed. Also, the printing problem can be avoided in another way, such as by presetting the number N to a relatively high value. However, when this number N is too high, the washing fluid could be continuously sprayed even after the rollers become clean. Therefore, the washing fluid and time are wasted, and the work efficiency problems remain.